Krzysztof Kowalczyk • 3/29/2026

Speeding up JavaScript function with AI help

This article explores optimizing a JavaScript function called isCJK() used for detecting CJK characters in text rendering. The author identifies performance bottlenecks in the original code, which uses multiple OR comparisons, and proposes an early exit for ASCII characters to reduce comparisons. The article details the optimization process, including mechanical sympathy, micro-benchmarking with warmup phases for JIT compilation, and using AI (Claude) to generate benchmark code. It emphasizes practical performance improvements for web apps.

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#JavaScript #performance optimization #benchmarking